Pain is one of the basic clinical symptoms. There is a worldwide need for effective pain treatments. The urgency of the requirement for therapeutic methods for providing tailored and targeted treatment of chronic and non-chronic pain, this being taken to mean pain treatment which is effective and satisfactory from the patient's standpoint, is evident from the large number of scientific papers relating to applied analgesia and to basic nociception research which have appeared in recent times.
Conventional opioids, such as for example morphine, are effective in the treatment of severe to very severe pain, but they exhibit unwanted accompanying symptoms, such as for example respiratory depression, vomiting, sedation or constipation or the development of tolerance. Moreover, they are less effective in treating neuropathic or incidental pain, which is in particular experienced by tumour patients.
Opioids exert their analgesic effect by binding to membrane receptors belonging to the family of G protein-coupled receptors. There are moreover further receptors and ion channels which play a role in the system governing the genesis and transmission of pain, such as for example the N-methyl-D-aspartate (NMDA) ion channel, via which a substantial proportion of synaptic communication proceeds and by which calcium ion exchange between neuronal cells and their surroundings is controlled.
Knowledge about the physiological significance of ion channel-selective substances has been obtained by the development of the patch-clamp technique with which the action of NMDA antagonists on the calcium balance in the cell's interior may be detected.